In an optical communication system, wavelength division multiplexing (WDM) may be used to multiplex a plurality of optical channels onto a single optical fiber. Each optical channel carries respective data at a different optical wavelength. Dense wavelength division multiplexing (DWDM) is one type of WDM that may be employed.
In a WDM system, it may be desirable to monitor the performance of the optical channels through optical performance monitoring. One way to perform optical performance monitoring is to use a respective pilot tone carried on each optical channel. A pilot tone is a small and relatively low-frequency modulation (e.g. kHz to MHz) applied to each optical channel. Each optical channel is modulated with a different pilot tone frequency. Each pilot tone may carry respective pilot data. The pilot data of each optical channel may be detected in various places of interest in the optical network and used to perform the optical performance monitoring. Also, the power of a particular pilot tone may be useful for estimating the power of the optical channel.
Reliable pilot data detection is desirable in both high signal-to-noise (SNR) conditions and low SNR conditions.